When Captain Sir John Lindsay returns to his young daughter Dido Belle after the death of her mother, a former slave, he proffers his love and care in the form of chocolate. This small gift represents a greater one: Lindsay recognises Dido as the legitimate heir to his name and fortune – a singular act in 1769 Britain, which, as the opening titles remind us, was “a colonial empire and slave trading centre”. The sweet mixture of sugar and cocoa from the colonies that Lindsay gives to his daughter is like the film’s use of costume drama: simultaneously drawing the viewer in and critiquing the ‘chocolate box’ style of the genre and its literary sources by revealing the bitter ingredients on which they depend.

The film opens with young Dido being laced into a corset; director Amma Asante neither casts out costume drama’s textural, architectural beauty in favour of the gritty approach of her first feature A Way of Life (2004), nor casts it at odds with a protagonist of colour. Rather, as the film’s title implies, beauty flows from and around Dido. With grace and assurance, Gugu Mbatha-Raw’s performance as the adult Dido centres the film, as vividly mobile as the depiction of the historical Dido Lindsay and her cousin Elizabeth Murray in the portrait, attributed to Johann Zoffany, that inspired the film. The painting is reputedly the first to depict a black subject sharing an equal eyeline with a white subject.

While putting Dido front and centre, Asante highlights the female relationships that are key to the genre, not only between the two cousins but also with the older women – their great-aunts Lady Mansfield and Lady Mary Murray, and the family’s London maid Mabel – who mother the motherless girls. As the film transforms the young Dido and Elizabeth into their older selves with an apparently seamless shot of them running around a tree, it also nods to the maze in Sally Potter’s Orlando (1992) and through it to a matrilineage of critical heritage dramas by Ruth Prawer Jhabvala, Julie Dash, Jane Campion, Patricia Rozema, Mira Nair and Andrea Arnold.

Belle (2014)

As in those films, in a clever twist on the Bechdel test, Asante shows that it is through talking about marriage and men that the female protagonists of costume drama are able to articulate a political philosophy, culminating here when Elizabeth states: “We are but their property.” Through the cousins’ entanglement with the socially superior but spendthrift Ashford family, Asante frankly depicts the classist, racist and sexist violence that contours the romantic fantasy. Dido’s insistence, even in the face of Oliver Ashford’s self-interested proposal and his brother James’s attempted sexual assault, that she is entitled to romance revivifies love as a structuring principle for her story, as does her eventual choice of beau. The son of a poor parish priest, John Davinier is a radical abolitionist clerking for Dido’s great-uncle Lord Mansfield, and the first person to see Dido as embodying her mother’s beauty rather than her father’s wealth.

When Davinier reveals to Dido the facts of the Zong case, on which Mansfield is sitting, she risks participation in a public as well as an intimate drama. The story of the Zong – a slave traders’ ship whose captain had his human cargo thrown overboard when supplies of water ran low – shocks Dido into a realisation of her anomalous position and its privileges. Making use of them, she hands Davinier papers that Mansfield has suppressed, in which the Zong’s first mate confesses the slaves were thrown overboard as an insurance scam.

Belle (2014)

This inextricable intertwining of love and justice, private and public, personal and political, is the film’s great cri de coeur and its structural brilliance, as costume and courtroom drama comment on, and merge into, each other. The film argues that Mansfield’s judgement, which found against the slavers and historically marked the beginning of the end of British slavery, must have been affected by the presence – forceful and articulate here – of his ward. Following her pivotal role in her great-uncle’s change of heart, Dido’s proposal to Davinier outside the Inns of Court after Mansfield’s verdict is akin to Cornel West’s assertion that “justice is what love looks like in public.”

“I have been blessed with freedom twice over, as a Negro and as a woman,” Dido tells Davinier, drawing an implicit line between the 18th century’s revolutionary notions of individual liberty and the civil-rights movements of the 20th. While Dido means, on the surface, that her legitimacy and inheritance have freed her from the constraints of her skin colour and gender, the statement suggests an exhilarating realisation: that it is from her marginalised position that she (and we) can have our chocolate and eat it, revelling in the film’s gorgeous awareness of what freedom truly means.